This invention relates to the measurement of fluid flow rate and/or total mass flow. The invention relates particularly, though not solely to measuring the flow rate and/or total mass flow of milk supplied during milking of cows. In this application the invention provides an electronic milk meter.
By "flow rate" it is meant liquid rate in mass unit time e.g. kg/min. By "total mass flow" it is meant the integration of flow over the measurement time.
When measuring the flow of, in particular, liquids which are not uniform in composition, such as, for example, the milk, delivered during machine milking which foams due to substantial and varying amounts of entrained air and other gases, an accurate determination of the flow rate or the total mass flow of liquid is difficult to achieve. With milk, because of the differing quantities of air and other gases contained within the milk, the density of the milk may change substantially during the milking process. An acceptable accuracy for total mass flow is within 2% of the actual yield of milk supplied. It has been found that it is difficult if not impossible to remove the gas from milk to an extent that will enable this accuracy to be achieved whilst measuring the milk volume during milking or very soon after the milking occurs. As one of the main purposes of measuring the total mass flow is to determine the milk yield from each animal substantial removal of gas would require the milk to be retained in individual cow portions for a substantial period of time. Clearly, this is impractical. A method proposed to overcome the problem of density variation in measuring milk volume is described in U.S. Pat. No. 5,035,139 where the foam profile of milk passing through a chamber is measured by measuring specific densities of the milk at different heights in the chamber. It would, however, be advantageous to measure total mass flow in a more direct manner rather than by making numerous volume and density measurements.